The present invention relates to a structural improvement of a trunnion of a toroidal type continuously variable transmissions used for vehicles.
An example of a link structure for supporting a trunnion of a toroidal continuously variable transmission is disclosed in Tokkai Hei 1-21261 published by the JapanesePatent Office.
In this toroidal type continuously variable transmission, a pair of power rollers is gripped between an input disk and an output disk arranged facing each other, and a rotation of the input disk is transmitted to the output disk via a power roller. The power roller is connected to a trunnnion via an eccentric shaft. When this trunnion moves in its axial direction due to an actuator, the power roller performs a swing motion essentially around the trunnion. The contact position of the roller relative to the input disk and output disk varies according to this oscillation angle, and the rotation ratio transmitted to the output disk from the input disk is therefore made to vary continuously.
The pair of power rollers is gripped between the input disk and the output disk. The magnitude of the rotation torque which can be transmitted is determined by the force with which the rollers are gripped. When this grip force is low, the power roller slips when a large torque acts, and the transmission efficiency of the disk rotation torque drops. It is most desirable that the rotation torque be transmitted equally by both power rollers, and for this purpose the grip pressures on both power rollers must be equalized. When the grip pressure acting on one power roller is low, the transmission torque is limited.
However, insofar as concerns the trunnion, each end of which is connected with a first and second links, a moment according to the direction of rotation acts on the pair of power rollers during power transmission, and the grip pressure on each power roller therefore can become different. Specifically, since the power rollers are arranged facing each other on either side of the rotation axis of the input and output disk, one power roller is pushed into between the input and output disk due to the moment accompanying the rotation, so that the grip force is high, but the other power roller is pushed out of the disks so that the grip force acting on it is low. The torque transmitted by each of the power rollers will therefore be different. Also even if the power rollers are fitted so as to cancel the influence of the aforesaid moment when the toroidal type continuously variable transmission is assembled, if there are still dimensional errors in the power roller fitting position, it will be impossible to set the grip pressure on both power rollers exactly according to design specifications. However, it is very difficult and very costly to completely eliminate dimensional errors.
It is therefore an object of the present invention to provide a toroidal type continuously variable transmission wherein the efficiency of transmitting a rotation torque is optimized.
The invention also effectively equalizes grip pressure on both power rollers by a simple structure, and provides a toroidal type continuously variable transmission which permits optimum transmission efficiency of rotation torque to be maintained.
Further, the invention provides a toroidal type continuously variable transmission which can equalize the grip pressures on the power rollers even when there is a dimensional error.
In order to achieve the above objects the invention provides a toroidal continuously variable transmission comprising a pair of coaxial input and output disks having toroidal conical surfaces facing each other, a pair of trunnions arranged in a plane perpendicular to the rotation axis of the input and output disks and each capable of displacement along an axis and around an axis, a power roller supported by the trunnion free to rotate about an eccentric axis in same, the power roller being gripped between the input and output disks, actuators for driving the pair of trunnions in mutually opposite axial directions, a first link connecting one end of each of the trunnions at opposite side of the actuators, the center part of this link being supported free to pivot about a first link supporting member, a second link connecting the other end of each of said trunnions, the center part of this link being supported free to pivot about a second link supporting member, adjusting means for permitting the displacement of the first or second link supporting member within predetermined limits so as to cause either the first or second link to displace within predetermined limits in the longitudinal direction of the link joining the pair of trunnions.
It is preferable that the adjusting means comprises an oblong hole for restricting the displacement of the first or second link supporting member within predetermined limits in the longitudinal direction of the link, a knock pin provided in the casing which passes through the adjusting hole, and tightening means for selectively fixing said link supporting member to the casing.
It is also preferable that the adjusting means comprises an oblong hole for restricting the displacement of the first link supporting member within predetermined limits in the longitudinal direction of the link, a bolt provided in the casing which passes through the adjusting hole and a pair of collars for gripping the first link supporting member.
It is also preferable that the adjusting means comprises a knock pin provided in either a body to which the actuators are fitted or the casing, an adjusting hole provided in the other of the body or casing for permitting displacement of the second link supporting member in the longitudinal direction of the link, and tightening means for selectively fixing the body to the casing.
It is also preferable that the actuators comprise means for permitting displacement within predetermined limits in a direction perpendicular to the axial direction.
It is also preferable that the actuators are hydraulic cylinders, the trunnions are driven in an axial direction due to the motion of pistons of the cylinders, and the means which permits displacement in a perpendicular direction to the axial direction comprises a gap in sliding parts between the cylinders and the pistons, and a seal ring for sealing this sliding gap.